A. have
B. has
C. had 
D. having

=A. work
B. worked
C. have worked
D. working

A. give
B. gave
C. gives
D. giving

A. wait
B. waiting
C. are waiting
D. waits

A. is
B. was
C. were
D. be

A. study
B. studies
C. studied
D. studying

A. has
B. have
C. had
D. was

A. is
B. are
C. was
D. were

A. open
B. opened
C. opening
D. opens

A. sing
B. sang
C. sung
D. singing